Making a thermosetting resin impregnating laminate

ABSTRACT

The present invention provides a process for making a thermosetting resin article which comprises (a) impregnating a compressible open-cell sheet with a thermosetting resin (b) applying a fibrous layer to at least one side of the sheet, (c) allowing the assembly to cure. The invention further is directed to thermosetting articles made by this process.

United States Patent [191 Goppel et a1.

[ 1 Oct. 28, 1975 MAKING A THERMOSETTING RESIN IMPREGNATING LAMINATEInventors: Johan M. Goppel; Peter R. Chant,

both of Delft, Netherlands Assignee: Shell Oil Company, Houston, Tex.

Filed: June 4, 1973 Appl. No.: 366,381

Related US. Application Data Continuation-impart of Ser. No. 208,937,Dec. 16, 1971, abandoned.

Foreign Application Priority Data June 26, 1970 United Kingdom 31101/70June 17, 1971 Belgium 3168 US. Cl. 156/313; 156/245; 427/429;

428/298; 428/417 Int. (Ll. C09,] 7/00 Field of Search 161/36, 37, 43,88, 93,

References Cited UNITED STATES PATENTS 3,193,435 7/1965 Schafer 161/159X 3,709,966 l/1973 Gambardella 161/159 X 3,726,708 4/1973 Weissenfelsl6l/l59 X FOREIGN PATENTS OR APPLICATIONS 1,209,974 10/1970 UnitedKingdom 1,068,503 5/1967 United Kingdom Primary Examiner-George F.Lesmes Assistant Examiner-Patricia C. Ives Attorney, Agent, orFirmNorris E. Faringer [57] ABSTRACT 8 Claims, No Drawings MAKING ATIERMOSETIING RESIN IMPRIEGNATING LANHNATE This application is acontinuation-in-part application of Ser. No. 308,937, filed Dec. 16,1971 now abandoned. Background of the Invention Field of the InventionThis invention relates to a method of producing an article ofthermosetting resin and to a novel thermosetting aricle.

Prior Art.

It is generally known in the laminating art that a laminated article canbe prepared by several methods. (1). In one method, a core of thedesired shape and density is pre-cut to the proper size and areinforcing layer, often a resin-reinforced glass layer, is then gluedon the core using the proper adhesive. If necessary, the assembly isthen placed in a mold and cured. (2). Another method, often referred toas the hand easy-up method, involves producing an article in or on amold. This method includes coating the molding surface with a releaseagent, laying a fibrous reinforcing material, for example, a layer ofglass fiber, on the molding surface, impregnating the fibrous layer withan uncured, liquid thermosetting resin, and allowing the resin to cureand harden. The liquid resin is conventionally applied by hadn. (3). Instill another method, particularly useful in the ski industry (seeArticle concerning K-2 skis in the Seattle Times, Jan. 31, 1971), thecore is pre-cut and a resin impregnated glass fiber mass is then wrappedaround the core, the assembly is placed in the mold and heated andpressured so that the resin properly cures. In this case, the resin actsnot only as an adhesive agent, but also the resin laminate combinationenvelopes the entire core.

Disadvantages of the first and third methods is that the core must bepre-cut exactly to fit the mold which is a time-consuming step,especially when working with difficult shapes such as skis. In the handeasyup method, the manual application of the resin is timeconsuming andcostly; moreover, the quality of the impregnated product is not the sameover different areas thereof as a result of non-uniform impregnationwith the resin.

It is generally known in the art that a foam sheet can be mildlyimpregnated with a thermosetting resin, partially compressed, and theresin allowed to cure in order to form a relatively strong, rigidarticle. Further, other materials, such as metals, wood, syntheticplastic material, or textile materials, can be used to face the resinimpregnated foam article either before or after molding the foam (seeGreat Britain Pat. No. 911,427, issued Nov. 28, 1962). It is also knownthat a thermosetting resin reinforced with a glass fiber mat (describedabove) can be laminated to a thermosetting resin impregnatedpolyurethane foam, the foam being employed to improve the surfaceappearance of the final article (see Great Britain Pat. No. 1,068,503,issued May 10, 1967). In these methods, it is necessary to form thefacing material separate from the impregnated foam and laminate the twothereafter.

It has also been suggested in British Pat. No. 1,209,974 to Konig,published Oct. 28, 1970, that an article is formed by mixingcompressible filler particles of foamed material with 'fibrousreinforcing material and a synthetic resin, then laying a fibrousreinforcing material on the mixture, and compressing the assembly todistribute the resin throughout the core and fibrous layer. However,this method requires that fibers be distributed in the core to get thedesired results.

SUMMARY OF THE INVENTION 5 This invention introduces an entirely newconcept into the art of preparing thermosetting resin articles, inparticular laminated articles, in order to overcome many of thedifficulties experienced in the prior art. The basis of the invention isthe utilization of a compressible open-cell sheet as a carrier for athermosetting resin so that a fibrous reinforcing layer is controllablyimpregnated with the resin.

Accordingly, the invention provides a method of producing an article ofthermosetting resin which comprises:

a. impregnating a flexible, compressible sheet having an open-cellstructure with a curable thermosetting resin,

b. applying a layer of fibrous reinforcing material to at least one sideof the impregnated sheet,

0. compressing the sheet and reinforcing layer to the extent that anyvoids remaining in the sheet after its impregnation with the resin areeliminated and resin is expelled from the sheet into the fibrousreinforcing layer so as to impregnate this layer with resin through itsthickness, and

d. allowing the resin in the sheet and layer to cure while maintainingthe compression.

Further, this invention provides a thermosetting resin 30 articlecomprising:

1. a thermosetting resin,

2. at least one fibrous layer which is uniformly impregnated with thethermosetting resin, and

3. a dense, visually solid layer substantially without voids, which isprepared by compressing .to less than 30% of its original thickness, aflexible, compressible, open-cell structured layer, in which at least25% of the open-cell space has been impregnated with the thermosettingresin, the impregnated fibrous layer being bound to the dense solidlayer through the cohesive and adhesive action of the thermoset resin.

The invention is particularly suitable for making large objects in arelatively short time, for example, for making hulls of boats, since itpermits large areas of the fibrous reinforcing material to beimpregnated at once, but also can be easily adapted to the preparationof small articles such as skis or tennis racket frames or handles.

The invention exhibits many advantages in both the process and theproduct as compared to the more traditional processes of manufacturingmentioned above.

Processing advantages of the present invention include the followingamong others:

1. Low molding pressures conventionally less than kg/cm and usuallyabout 1 kg/cm so that even when two-part molds are employed, the mold,press and appurtenant apparatus investment costs are low.

2. Simplicity and convenience of working with easily handled materialsof construction.

3. Only one layer of any laminate the reservoir has to be impregnatedbefore lay-up in the press or die.

4. Easy lay-up even in complex molds since the compressible foamreservoir readily follows the mold contour.

5. Elimination of the need to lay-up additional material in places whereincreased stiffness or thickness is desired.

6. Cleaner, simpler and less labor dependent than laminate manufactureby hand lay-up, spray lay-up or vacuum/pressure bag molding so thatultimate product quality is considerably less dependent on operatorskill.

Product advantages briefly include:

1. A wide range of performance characteristics is obtainable so thatdesign requirements can be met accurately and economically.

2. Stiffness and thickness are located precisely when required andoptimum use can be made of the reinforcement. Thus, a distinctivefeature is that the quantity of reinforcement and the thickness of thelaminate are variable independently of each other since the thickness ofthe laminate can be altered within wide limits by changing the thicknessof the compressed foam core, keeping the reinforcement constant.Alternatively, the type and quantity of reinforcement can be changedwithout changing composite thickness.

3.Specific quantities are low, producing high stiffness to weightratios.

DESCRIPTION OF THE PREFERRED EMBODIIVIENTS The thermosetting resinssuitable for use in this process includes phenolics, melamines,polyesters, epoxies and silicones. Generally, it is found that polyesterand epoxy resins are eminently suitable in this particular process andfor this reason are preferred. The thermosetting resins are converted tothe thermoset form by cross-linking processes usually accomplished bythe addition of a curing agent, with or without one or more curingcatalysts or accelerators, to the resin. Proper curing agent for epoxyand polyester resins are well known to those skilled in the art. See,for example, chapters 5-12 of the Handbook of Epoxy Resins, Lee andNeville, McGraw Hill, Inc. 1967, for curing agents and mechanisms ofcure for epoxy resins and chapter 6 of Rineholt Plastic ApplicationSeries, polyester resins, Lawrence, Rinehold Publishing Corp., 1967 forcuring agents and mechanisms of cure for polyester resins. The resinswill be in the liquid form so that the opencell sheet can be properlyimpregnated. Of the epoxy resins, particularly preferred are the liquidglycidyl polyethers of polyhydric phenols, such as the diglycidyl etherof bisphenol A (BPA) made by reacting epichlorohydrin and BPA in thepresence of caustic and generally having a molecular weight of about 350to 400 and an epoxide equivalent of about 180 to 200. The preferredpolyesters are the unsaturated polyesters generally known to be used inthe laminating art.

The fibrous reinforcing layer used in the process of this invention canbe one of many of the reinforcing layers known in the art such ascellulosic paper; cotton fabric; asbestos paper and fabric; nylonfabric; glass paper, mat or fabric; and metal filaments. The particularchoice of reinforcing material, of course, will depend on the degree ofstiffness required for the finished article. Particularly useful isglass and asbestos; reinforcing with glass paper, mat or fabric beingpreferred. Instead of only one fibrous layer, two such layers may beapplied to the foam sheet, one on each side thereof. The foam sheetshould then contain sufficient resin and be sufficiently compressed toimpregnate both fibrous layers adequately. It is also possible to formthe article from an assembly comprising two or more impregnated foamsheets alternating with fibrous layers.

The sheet having open-cell structure acts as the use ervoir for theresin as well as the foam core for the Elk ished thermosetting resinarticle. This sheet or layer can be referred to as the reservoir sheet.Generally, the sheet having the open-cell structure should be highlycompressible, flexible, readily wettable by the liquid resin, and mustpossess an open connected cellular structure to allow essentiallyunobstructed passage of the liquid resin throughout the sheet. Sheetswhich are particularly useful in this regard include sheets of battingof natural or synthetic materials as long as the material does not reactwith the thermosetting resin which is used to impregnate the sheet, thuscotton batting is usable in this particular process. However, it ispreferable to use a foam sheet which has an open-cell structure which issuitably made of a thermoplastic material, polyurethane, or elastomer.Polyurethane is particularly useful in this regard.

A sheet of flexible foam material can be immersed in a bath containingthe liquid resin and be compressed in the bath by passage betweencompression rolls to drive out air from the cellular space of the foamthereby allowing the resin to fill the cellular space. If desired, thesoaked sheet after leaving the bath may be passed between another set ofrolls to reduce the volume of resin held by the sheet. However, it isgenerally desirable that the sheet is impregnated with resin, so as tofill at least 25% of the open cell space of the uncompressed sheet, andsuitably about 35% or more. A particularly useful method of impregnationinvolves supplying foam sheet from two oppositely disposed supplysources, converting the two foam sheets supplied between a set ofcompression rolls so that the sheets are compressed to the desireddegree, and supplying the liquid resin at the point of conveyance alongthe width of the sheets where the foam sheets contact so that the resinis soaked up by the expansion of the foam sheets after leaving thecompression rolls. By this method a reservoir sheet of resin is formedwherein the outer face of the sheet is drier than the immersionimpregnated foam sheets and thus easier to handle.

It is sometimes advantageous to partially cure the resin in theimpregnated sheet to the B-stage then wind the B-Staged impregnatedsheet on a roll for storage. This also aids in the handling of thereservoir sheet.

After the foam sheet has been impregnated to the desired degree, a layerof fibrous reinforcing material is applied to a side of the sheet. Inpractice, the assembly formed by the foam sheet and fibrous layer may beprepared outside of a mold and then be transferred to the mold andplaced in contact with the molding surface. Alternatively, the fibrouslayer is first laid on the molding surface, and the impregnated foamsheet is then applied to the fibrous layer. In both cases, it may befound desirable to allow the resin in the foam sheet to cure partlybefore the sheet is placed in the mold. If the resin is partly cured,for example, to the B-stage, the increased viscosity of the resin makesthe sheet easier to handle. The B-stage is an early stage of cure beforeall the molecules are cross-linked where the resin exists as t athermoplastic which is hard but frangible and soluble in solvents suchas acetone.

The next step is the application or pressure to the assembly,as,for'example, by pressing another molding surface against theassembly,'The pressure should be sufficient to compress the foam sheetto the extent that any open spaces in the impregnated foam sheet areeliminated as-far as possible and resin from the sheet is squeezed outfrom the sheet into the fibrous layer whereby this layer is thoroughlyimpregnated through out its thickness. The degree of compression of thefoam sheet depends on the volume of resin taken up by the sheet duringimpregnation and the volume of resin required to impregnate the fibrouslayer. Generally, only very low pressures are needed, i.e., less thankg/cm or less and usually only about 1 kg/cm is needed. usually it willbe necessary to compress the foam sheet to or less of its originalthickness. While the pressure is maintained, the resin in the compressedassembly is allowed to cure and thereby to become hard, whereafter thepressure can be released and the article formed by the hardened assemblycan be removed from the mold. It is to be noted that the compressed andhardened sheet in the article has no longer an opencell foam structure,but instead has turned into a dense and visually solid layer withoutvoids, and accordingly, this layer is not comparable with resin-wettedfoamed plastics materials which have been hardened without theapplication of compression.

The compression of the foam sheet and fibrous layer may be appliedselectively over their surface so that the combined thickness of thecompressed sheet and layer is not uniform. Accordingly, when using afoam sheet and a fibrous layer of originally uniform thickness, it ispossible to form the article with indentations 0r elevations as may bedesired for shaping or for strength.

The method of the invention will normally be practiced using a mold,which may have a straight, curved or profiled molding surface asrequired. However, if the article to be made is, for example, a rigidsheet or board, it is possible to continuously pass the impregnated foamsheet with fibrous layer between compression means which apply therequired compression to the assembly wherein during the passage theresin is cured. The compression means can be formed by rolls or by twoopposite endless belts or by an adjustable or fixed metal, preferablysteel die. To ensure that the resin has hardened before the assemblyleaves the compression means a fast-curing resin composition can beselected, and/or heat may be supplied to the resin, for example, byemploying heated compression means to shorten the curing time.

Particularly useful in this regard is to use a pultrusion method whereinthe compression is applied by passing foam sheet and reinforcing layerthrough a forming die, and during said passage the resin in the sheetand layer is allowed to cure. The forming die, preferably a slitshapeddie with a tapering entrance, serves simultaneously as a compressiondevice for driving out resin from the foam sheet into the reinforcinglayer and as a shaping device for forming the assembly composed of thefoam sheet and reinforcing layer, into the shape of the desired article.This pultrusion method is particularly useful for making shapes withhigh unidirectional strengths such as flat and profile stock forbuilding siding and facia, i and other beams, gutters and down spoutspiping, fishing rods, golf clubs, arrow shafts and the like. ()neadvanta e to this method is that it is continu'ous; consequently, theneed for molds being periodically opened and closed is eliminated.

By using a tapered entrance for the die, the compression of the foamsheet can be effected in a gradual and controlled manner to ensureuniform and thorough impregnation of the reinforcing layer with resins.The foam sheet and reinforcing layer may be fed into the die in flatcondition or in a'curved shape, depending on requirements. The die maybe designed so as to shape the compressed assembly in the form of asheet, pipe, profiled beam or other article desired. To prevent drool atthe entrance of the die or to increase the rate of production, the resinin the foam sheet can be partly cured to the Bstage before feeding thesheet into the die.

This aspect of the invention is, for example, carried out by covering asheet of foamed, flexible, open-cell polyurethane impregnated with athermosetting resin on both sides with a glass-fiber mat then passingthe covered impregnated sheet through a forming die composed of lowerand upper die sections (optionally with linings of tetrafluoroethylene)with a tapering entrance to allow the uncompressed covered sheet toeasily enter. The sheet is gradually compressed as it passes through theentrance to a slit-shaped section having parallel flat walls. The diemay be open-ended laterally. A traction device is provided at the exitof the die to pull the assembly through the die in a continuousmovement. Electrical heaters or other heating devices are easily mountedin the forming die at one or both sides of the die and/or entrance. Theupper and lower die sections may be adjustable relative to each other toadjust the spacing therebetween. The length of the die should besufficient to ensure complete curing of the assembly before it leavesthe die for the desired speed of operation and curing temperature.

To illustrate the manner in which the invention may be carried out, thefollowing embodiments are given. it is to be understood, however, thatthese embodiments are for the purpose of illustration and the inventionis not to be regarded as limited to any of the specific materials orconditions recited therein.

ILLUSTIVE EMBODIMENT l A sheet of flexible foamed polyurethane with athickness of 10 mm was soaked in an epoxy resin system and passedbetween rollers to squeeze out the excess of resin, so that about 2 kgresin remained in the sheet per in surface area.

The impregnated sheet was B-staged for seconds at 180C.

A glass fiber mat was placed on one side of the sheet, the laminateassembly was placed in a hot mold (180C) and pressure was applied forseconds.

The final thickness of the laminate was 2-3 mm.

lLLUSTlVE EODIMENT II A 20 mm thick sheet of open-celled flexiblepolyurethane foam was impregnated with liquid epoxy resin by passagethrough a bath containing the resin. In the bath, the sheet wascompressed followed by expansion to soak it with the resin. 0n leavingthe bath, the sheet was passed through a pair of squeeze rollers toexpel excess resin. After this operation, the sheet contained 1.2 kg ofresin per in of surface area. The impregnated sheet was transported on acontinuously moving conveyor belt through an oven maintained at C, theresidence time of the sheet in the oven being 75 seconds. At thismoment, the resin in the foam had cured to the B-stage. A glass fibermat was then placed on both sides of the sheet, and the assembly was fedinto a forming die having a tapered entrance 1000 mm long and 25 mm wideat the widest point and having a parallel die section 200 mm long and 2mm wide (both lengths measured parallel to the direction of movement ofthe assembly while both widths are normal to the direction of the sheetassembly).

The parallel section of the die was maintained at 180C, and the assemblywas pulled through the die with a speed of 30 cm/min. Thus the residencetime was 40 seconds during which the resin in the assembly had curedcompletely and a 2 mm thick rigid laminate emerged from the die.

We claim as our invention:

1. A process for producing an article of thermosetting resin,comprising:

a. impregnating a compressible sheet having an opencell foam structurewith a liquid heat-curable thermosetting resin,

b. applying at least one layer of fibrous reinforcing material on bothsides of the impregnated foam sheet,

c. compressing the foam sheet and reinforcing layers to the extent thatany voids remaining in the sheet after its impregnation with the resinare substantially eliminated and resin is expelled from the foamed sheetinto the fibrous reinforcing layers impregnating said fibrous layerswith resin throughout its thickness, and

(1. allowing the resin in the sheet and layers to cure to a unitarystructure while maintaining the compression.

2. The process of claim 1 wherein after the reinforcing layers have beenapplied to the foam sheet, the resulting assembly is placed in contactwith a molding surface, and the assembly is compressed against saidmolding surface.

3. The process of claim 1 wherein the resin in the foam sheet is allowedto cure partly before the sheet and layers are compressed.

4. The process of claim 1 wherein the impregnated foam sheet iscompressed to 30% or less of its original thickness.

5. The process of claim 1 wherein the compression is appliedselectively, so that the combined thickness of the compressed sheet andlayers are not uniform over their surface.

6. The process of claim 1 wherein the foam sheet is impregnated with theresin, so that at least 25% of the open cell space of the sheet isfilled.

7. The process of claim 1 wherein the compressing is done bycontinuously passing the impregnated foam sheet and fibrous layersbetween compression means during which passage the resin is cured.

8. The process of claim 7 wherein the compression means is a fixed metaldie.

1. A PROCESS FOR PRODUCING AN ARTICLE OF THERMOSETTING RESIN,COMPRISING: A. IMPREGNATING A COMPRESSIBLE SHEET HAVING AN OPEN-CELLFOAM STRUCTURE WITH A LIQUID HEAT-CURABLE THERMOSETTING RESIN, B.APPLYING AT LEAST ONE LAYER OF FIBROUS REINFORCING MATERIAL ON BOTHSIDES OF THE IMPREGNATED FOAM SHEET, C. COMPRESSING THE FOAM SHEET ANDREINFORCING LAYERS TO THE EXTENT THAT ANY VOIDS REMAINING IN THE SHEETAFTER ITS IMPREGNATION WITH THE RESIN ARE SUBSTANTIALLY ELIMINATED ANDRESIN IS EXPELLED FROM THE FOAMED SHEET INTO THE FIBROUS REINFORCINGLAYERS IMPREGNATING SAID FIBROUS LAYERS WITH RESIN THROUGHOUT ITSTHICKNESS, AND D. ALLOWING THE RESIN IN THE SHEET AND LAYERS TO CURE TOA UNITARY STRUCTURE WHILE MAINTAINING THE COMPRESSION.
 2. The process ofclaim 1 wherein after the reinforcing layers have been applied to thefoam sheet, the resulting assembly is placed in contact with a moldingsurface, and the assembly is compressed against said molding surface. 3.The process of claim 1 wherein the resin in the foam sheet is allowed tocure partly before the sheet and layers are compressed.
 4. The processof claim 1 wherein the impregnated foam sheet is compressed to 30% orless of its original thickness.
 5. The process of claim 1 wherein thecompression is applied selectively, so that the combined thickness ofthe compressed sheet and layers are not uniform over their surface. 6.The process Of claim 1 wherein the foam sheet is impregnated with theresin, so that at least 25% of the open cell space of the sheet isfilled.
 7. The process of claim 1 wherein the compressing is done bycontinuously passing the impregnated foam sheet and fibrous layersbetween compression means during which passage the resin is cured. 8.The process of claim 7 wherein the compression means is a fixed metaldie.